1. Field of the Invention
The present invention generally relates to a light source of a back light module for illuminating a liquid crystal display, and more particularly, the present invention relates to a light source that produces a white light through mixing red, green and blue lights.
2. Description of the Related Art
To match the modern life style, video or imaging device needs to be lighter and slimmer. Although the conventional cathode ray tube (CRT) display has many advantages, the design of the electron gun renders it heavy and bulky. Moreover, there is always some risk of radiation emitted by the conventional cathode ray tube hurting viewer″s eyes. With big leaps in the techniques in manufacturing semiconductor devices and electro-optical devices, flat panel displays such as liquid crystal displays (LCD), organic light-emitting displays (OLED) and plasma display panel (PDP) have gradually become mainstream display products.
According to the light source, a liquid crystal display can be classified as belonging to one of the three types, namely, a reflection LCD, a transmissive LCD and a transflective LCD. Using a transmission or a transflective LCD as an example, the LCD mainly comprises a liquid crystal panel and a back light module. The back light module provides a plane light source to illuminate the liquid crystal panel for displaying images.
The light source of a conventional back light module is either a fluorescent lamp or a set of light-emitting diodes. If light-emitting diodes are used as the light source in a back light module, white light is produced through a mixing of the red (R), green (G) and blue (B) lights emitted from various diodes. In the conventional technique, red, green and blue light-emitting diodes are laid flat on a surface so that the red, green and blue lights from various light-emitting diodes can mix together to form a plane light source that emits white light.
However, due to the limitation caused by the light dispersion angle of a light-emitting diode, red, green and blue lights from the light-emitting diodes are mixed into white light at a distance of more than a few centimeters above the original sources. This constrains the size of a back light module design. Another problem that results from mixing red, green and blue lights to produce white light is that there is a significant difference in the measured spectrum distribution of white light according to the location. In other words, the spectrum of the white light produced through mixing of red, green and blue lights is highly non-uniform.